1. Technical Field
The present invention generally relates to a method of removing an effect of side lobes, and more particularly to a method of reducing an effect of side lobes with a relative low amount of calculations in forming an ultrasound synthetic image for a moving object to thereby enhance resolution and improve a signal-to-noise ratio (SNR).
2. Background Art
Generally, an ultrasound diagnostic system may use an array transducer for transmitting and receiving ultrasound signals. In order to obtain an enhanced ultrasound image, an ultrasound synthetic image may be adopted. The ultrasound synthetic image may be formed by using receive dynamic focusing for forming multi-receive beams in response to one time transmission of a transmit beam. The ultrasound diagnostic system may synthesize the receive beams corresponding to the same scan line obtained through a plurality of transmissions of the transmit beam along a plurality of scan lines to thereby form an ultrasound synthetic image. For example, assuming that the transmit beam is transmitted along a nth scan line (Sn), the ultrasound diagnostic system may form (2m+1) numbers of receive beams corresponding to scan lines Sn−m, Sn−(m−1), . . . , Sn, . . . , Sn+(m−1), Sn+m, wherein m>0. As shown in FIG. 1, when the transmit beam is focused along a scan line Sn, three receive beams may be formed based on echo signals from scan lines Sn−1, Sn and Sn+1. That is, three receive beams may be obtained per each scan line and the receive beams are then synthesized to form an ultrasound synthetic image.
When a target object is a stationary object, an ultrasound synthetic having good resolution and signal to noise ration may be obtained. However, when the target object is a moving object (especially moving in an axial direction), an undesirable image may be displayed in forming an ultrasound synthetic image. That is, the ultrasound synthetic image may be formed by using receive beams obtained with a time delay or multiple transmit beams such as bi-directional pixel based focusing. Thus, if a motion occurs in the target object and beam forming is carried out without considering the motion, then an incoherent sum may occur, which makes contrast resolution and SNR lowered.
Various pixel based researches or area based researches have been conducted in order to estimate and compensate a motion that occurred in the ultrasound synthetic image. There are proposed methods for estimating and compensating the motion by using cross correlation, auto correlation, sum of absolute difference, etc. There is a problem in that the pixel based motion estimation and compensation requires a large amount of calculation.